Isoprene

Isoprene is a common synonym for the chemical compound 2-methylbuta-1,3-diene. It is commonly used in industry, is an important biological material, and can be a harmful environmental pollutant and toxicant when present in excess quantities.

At room temperature, isoprene is a colorless liquid which is highly flammable and easily ignited. It can form explosive mixtures in air and is highly reactive, capable of polymerizing explosively when heated. The United States Department of Transportation considers isoprene a hazardous material and requires special marking, labeling, and transportation for it.

It is most readily available industrially as a by-product of the thermal rubber.

Natural polymer of isoprene - most often cis-1,4-polyisoprene - with a molecular weight of 100,000 to 1,000,000. Typically, a few percent of other materials, such as proteins, fatty acids, resins and inorganic materials are found in high quality natural rubber.

Some natural rubber sources called isomer which has similar, but not identical properties.

Biological roles and effects

Isoprene is formed naturally in animals and plants and is generally the most common µmol/kg/h, equivalent to approximately 17 mg/day for a 70 kg person. Isoprene is also common in low concentrations in many foods. Isoprene is produced in the chloroplasts of leaves of certain tree species through the DMAPP pathway; the enzyme isoprene synthase is responsible for its biosynthesis. The amount of isoprene released from isoprene-emitting vegetation depends on leaf mass, leaf area, light (particularly photosynthetic photon flux density), and leaf temperature. Thus, during the night, little isoprene is emitted from tree leaves while daytime emissions are expected to be substantial (~5-20 mg/m2/h) during hot and sunny days.

With a global biogenic production in the range of 400–600 Tg of carbon/year, isoprene has a large impact on atmospheric processes and is thus an important compound in the field of mechanistic studies of isoprene oxidation via OH radicals, ozone, and NO₃ radicals.

It is a common structural motif in biological systems. The squalene and hence from isoprene. The functional isoprene units in biological systems are dimethylallyl pyrophosphate (DMAPP) and its isomer isopentenyl pyrophosphate (IPP), which are used in the biosynthesis of terpenes and lanosterol derivatives.

In virtually all organisms, isoprene derivatives are synthetised by the isoprenylation.

According to the United States Department of Health and Human Services Eleventh Edition Report on Carcinogens, isoprene is reasonably expected to be a human carcinogen. Tumors have been observed in multiple locations in multiple test species exposed to isoprene vapor. No adequate human studies of the relationship between isoprene exposure and human cancer have been reported.

Biosynthesis and its inhibition by statins

HMG-CoA reductase inhibitors, also known as the group of cholesterol-lowering drugs called statins, inhibit the synthesis of mevalonate. Mevalonate is a precursor to isopentenyl pyrophosphate, which combines with its isomer, dimethylallyl pyrophosphate, in repeating alternations to form isoprene (or polyprenyl) chains.

Statins are used to lower coenzyme Q10. This flow chartshows the biosynthesis of isoprenes, and the point at which statins act to inhibit this process.

References

• Merck Index: an encyclopedia of chemicals, drugs, and biologicals, Susan Budavari (ed.), 11th Edition, Rahway, NJ : Merck, 1989, ISBN 0-911910-28-X
• Poisson, N.; M. Kanakidou, and P. J. Crutzen (2000). "Impact of nonmethanehydrocarbons on tropospheric chemistry and the oxidizing power of the global troposphere: 3-dimensional modelling results". Journal of Atmospheric Chemistry 36 (2): 157–230. doi:10.1023/A:1006300616544. ISSN 0167-7764.
• Monson, R. K.; and E. A. Holland (2001). "Biospheric trace gas fluxes and their control over tropospheric chemistry". Annual Review of Ecology and Systematics 32: 547-576. doi:10.1146/annurev.ecolsys.32.081501.114136.
• Claeys, M.; B. Graham, G. Vas, W. Wang, R. Vermeylen, V. Pashynska, J. Cafmeyer, P. Guyon, M. O. Andreae, P. Artaxo, and W. Maenhaut (2004). "Formation of secondary organic aerosols through photooxidation of isoprene". Science 303 (5661): 1173-1176. doi:10.1126/science.1092805. ISSN 0036-8075.
• Pier, P. A.; and C. McDuffie (1997). "Seasonal isoprene emission rates and model comparisons using whole-tree emissions from white oak". Journal of Geophysical Research 102 (D20): 23,963–23,971. ISSN 0148-0227.
• Poschl, U.; R. von Kuhlmann, N. Poisson, and P. J. Crutzen (2000). "Development and intercomparison of condensed isoprene oxidation mechanisms for global atmospheric modeling". Journal of Atmospheric Chemistry 37 (1): 29–52. doi:10.1023/A:1006391009798. ISSN 0167-7764.
• Guenther, A.; T. Karl, P. Harley, C. Wiedinmyer, P. I. Palmer and C. Geron (2006). "Estimates of global terrestrial isoprene emissions using MEGAN (Model of Emissions of Gases and Aerosols from Nature)". Atmos. Chem. Phys. 6: 3181-3210.